11.5 Downgrade Troubleshooting

If you downgrade from one release series to another, there may be
incompatibilities in table storage formats. In this case, use
mysqldump to dump your tables before
downgrading. After downgrading, reload the dump file using
mysql or mysqlimport to
re-create your tables. For examples, see
Section 10.11, “Copying MySQL Databases to Another Machine”.

A typical symptom of a downward-incompatible table format change
when you downgrade is that you cannot open tables. In that case,
use the following procedure:

Stop the older MySQL server that you are downgrading to.

Restart the newer MySQL server you are downgrading from.

Dump any tables that were inaccessible to the older server by
using mysqldump to create a dump file.

Stop the newer MySQL server and restart the older one.

Reload the dump file into the older server. Your tables should
be accessible.